Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor including one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
The rotor blades are the primary elements for converting wind energy into electrical energy. Further, the rotor blades have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
Conventional rotor blades typically include a suction side shell and a pressure side shell that are bonded together at bond lines along the trailing and leading edges of the blade. An internal shear web extends between the pressure and suction side shell members and is bonded to spar caps affixed to the inner faces of the shell members. A typical wind blade includes a single web design which promotes torsional rigidity. Skin plies on the outer periphery of the airfoil also aid in increasing torsional rigidity. The shear web(s) may also promote stability of the flanges of the I-beam configuration of a spar cap system.
Additionally, the rotor blade can experience increased twist when the chord and thickness of the airfoil are reduced and the torsional stiffness of the blade starts dropping quickly. Such events typically start at an outboard location of the rotor blade, e.g. starting at about 50% span. Further, the blade tip generally experiences the greatest amount of twist, thereby changing the angle of attack in the wind, which can impact the energy capture of the rotor blade.
Accordingly, the industry would benefit from an improved rotor blade having an increased torsional stiffness without unduly increasing the weight thereof.